The bill would establish far-reaching goals: Californians would double energy efficiency in existing buildings; obtain half their electricity from renewable sources; and reduce petroleum use by 50 percent, all by 2030.

Not surprisingly, lobbyists for alternative energy providers, environmental groups, health advocates and many others declared their fealty to the bill. Nor was it surprising that the Senate Energy Committee approved the measure by an 8-3 party-line vote. De Léon is, after all, the Senate leader.

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“Just in case there is anybody left in the state of California to oppose the bill, is there anybody in opposition to the bill?” Senate Energy Committee Chairman Ben Hueso, a San Diego-area Democrat, asked with a slight grin.

Up stepped Eloy Garcia, lobbying for the Western State Petroleum Association. Again, not a shock that the trade group for oil producers opposes the legislation. It would strike at the core of the oil industry’s business.

We don’t doubt de Léon’s fundamental point that California and the rest of the world should reduce reliance on fossil fuels. But Garcia raised a point that ought to be discussed as this important bill wends its way through the legislative process: How exactly will California reduce its dependence on oil by half in the next 15 years?

California motorists consume about 16 billion gallons of gasoline and diesel fuel annually. To reduce that by 50 percent, we’d be using gasoline at levels that date to Ronald Reagan’s first year as governor, when there were 19 million Californians, not 38.8 million.

As the Senate staff analysis says, “the bill prescribes little for the achievement of the petroleum reduction,” except to cede the work of implementing the 50 percent petroleum reduction to the California Air Resources Board.

The powerful board is headed by Mary Nichols, a forward-thinking official with a strong environmentalist bent. The board has a well-deserved reputation for producing good work. But Democrats who control the Legislature had few probing questions at the Senate Energy Committee hearing.

The air board further assumes that Californians could reduce the rate of increase in vehicle miles traveled to 4 percent a year, raise fuel efficiency to 35 miles per gallon in cars and 7 miles per gallon in trucks, and double the number of vehicles that use alternative fuels. It sounds simple. It won’t be.

The price of electric vehicles remains beyond the reach of most Californians. Notions of people living close to where they work, using public transit and bicycles are nice, too, though not yet functional for many people.

Before they approve this far-reaching legislation, lawmakers need to get answers to basic questions, and let the rest of us in on the details.